Fix get_user auth issue

[zrnsm]

This example produces the following when launched in filter mode:

Traceback (most recent call last):
  File "streamwatcher.py", line 91, in <module>
    main()
  File "streamwatcher.py", line 75, in main
    user = tweepy.API().get_user(username)
  File "build/bdist.linux-x86_64/egg/tweepy/binder.py", line 239, in _call
  File "build/bdist.linux-x86_64/egg/tweepy/binder.py", line 189, in execute
tweepy.error.TweepError: Failed to send request: local variable 'auth' referenced before assignment

This seems to be because we're not passing auth when constructing the API.